1. Field of the Invention
The present invention relates to impact resistant compositions comprising novel crude graft polymers of vinylchloride on unsaturated olefinic elastomers, said elastomers being copolymers of ethylene with an .alpha.-olefin and a cyclic or acyclic diene or polyene, and a method for their preparation.
2. Prior Art
Impact resistant materials based on crude products of vinyl chloride grafted onto olefinic elastomers are already known. These materials, although providing manufacturated articles of high impact resistance and resistance to aging, have, however, the disadvantage of being difficult to process in the techniques normally used in the transformation of polyvinyl chloride into manufactured articles. Moreover, these materials lead to products having substantial surface unevenness which practically precludes the possibility of using such articles.
The poor processability (workability) of the known high impact materials is evidenced by their low flowability in the molten state (melt index).
For example, the crude graft products which may be prepared by means of the known processes, and containing from 8 to 10% by weight of total olefinic elastomer, never have melt index values higher than 1 (measurement carried out according to ASTM-D 1238 at 185.degree.C, with a load of 23.5 kg).
The methods heretofore used for the preparation of the above mentioned impact resistant materials comprise graft polymerizing vinyl chloride in the presence of an unsaturated olefinic rubber, until almost conversion of the monomer has occurred.
One of these methods is, for example, described in Italian Pat. No. 698,014 in the name of the assignee hereof. The method comprises polymerizing vinyl chloride in the presence of the olefinic rubber dissolved in the monomer, until a particularly high conversion rate has been obtained, and, in any case, greater than 75% conversion.
The crude products which are obtainable by the method described in said Italian patent consist of mixtures comprising the following fractions that are separatable by extraction with solvents:
A. VINYL CHLORIDE HOMOPOLYMERS,
B. UNMODIFIED OLEFINIC RUBBER, AND
C. A "REAL" GRAFT COPOLYMER OF RUBBER AND VINYL CHLORIDE (A COPOLYMER LACKING FREE RUBBER AND VINYL CHLORIDE HOMOPOLYMERS).
In these crude products the content of grafted polyvinyl chloride is particularly high, and is generally greater than 45 - 50% by weight with respect to the weight of the graft copolymer.